2016 Cultural Debate: Was it more mid 2010s or late 2010s?

Yeah. Just like with every year that ends with '6,' the first 3 quarters feel like the mid part of the decade, while the 4th quarter feels like the late part of the core decade.

Early-Mid 1986: Mid-80s part 1 (New Wave Era). Late 1986: Mid-80s part 2 (Hair metal Era).

Early-Mid 1996: Mid 90s (Grunge/16-Bit era). Late 1996: Late Core 90s (3D/Pre-Y2K Era).

Early-Mid 2006: Mid 2000s (CRT/WB/PS2 Era). Late 2006: Late Core 2000s (Flatscreen/CW/HD Gaming Era)

Early-Mid 2016: Mid 2010s (Hipster/Vine/Obama Era). Late 2016: Late Core 2010s (Trump/Trap Era).

yupp thats how it usually goes, in 2006 it was more noticeable because of every game trying to be realistic, I remember playing Sonic 2006
for Xbox 360 and laughing at how the whole game is like gritty and TOO realistic compared to games of the year before like it that had a cartoony feel.
That and Facebook launched without the need for a school e-mail, I had it but didn't really use it until a few months later.

I view mid 2013- September 2016 as one era

Ehh, kinda. In late 2016, as soon as the 2016-2017 school year started, it's like things shifted. Music got a little bit darker, the Weeknd went for a darker mood with Starboy, EDM got a little tamer if you listen to Starving by Zedd, and Mumble rap took over pop and EDM. iOS 10 got released, and while its mostly identical to iOS 7-9, it is more on the bubbly side instead of just full on flat. Movies got a little darker with Arrival and Suicide Squad. Then, the darkening process was complete by November when Trump got elected, Vine announcing their shutdown, PS4 Getting released, Stranger Things, you get the idea.

To me, both are more similar to each other than 2010 or 2011, maybe even 2012.

Early 2017 seemed like the mid-2010s ended and the late 2010s began, I agree. The 2016-17 school year felt like a sudden change...

This, I agree.